A lot of folks that hoard have mental issues, sometimes from a very poor childhood where they didn't have anything of their own. Others do it after a traumatic episode like a death. No matter what the reason, it makes no sense if 90% of the stuff is useless. I know of a couple people that started out as small time "preppers" and have slowly turned into hoarders. Most of the stuff they have is buried under other junk, and is useless due to that very problem. One person needed a generator a while back and couldn't dig it out of their garage to use it. I thought it might dawn on them how dumb that is, but it didn't slow them down.
